The linear FG and BG compositing system of the blue screen type has been described in my prior U.S. Pat. Nos. 3,595,987; 4,007,487; 4,100,569; 4,344,085; 4,409,611; and in a recent application (June 13, 1983) Ser. No. 520,067, which describes the origination and series of improvements in the compositing of video images using a linear technique.
This new technology combines the two images by first removing the color of the colored backing by a subtraction process, leaving the subject as though placed in front of a black backing. The background (BG) scene is then turned on in the area formerly occupied by the colored backing in proportion to the brightness and visibility of that colored backing. This proportional control of the BG scene permits the full and accurate retention of transparent and semi-transparent objects including smoke, fog, glassware, etc.
Since the foreground (FG) video is never subjected to a switching action, the ultimate resolution of the FG camera is retained in the composite scene. The aforementioned patents fully describe this technology, and are incorporated herein by reference. The process by which the color of the backing is removed is by subtraction and, as indicated in the above patents, may occur prior to encoding or subsequent to encoding.